1. Field of the Invention
The present invention relates to an incandescent type electric lamp, such as a halogen lamp, with a coiled-coil filament.
2. Description of Related Art
Incandescence electric lamps comprising the respective coiled-coil filaments are widely used in the field of small-sized lighting that requires high lighting intensities. In particular, it is known that the high efficiency of the light radiation effect can be obtained by using it with a reflector. Such an incandescence electric lamp may be used, for example, as a backlight to be equipped in a projector or the like or used as a heat source of rapid thermal processing (RTP) for a semiconductor device. Here, the coiled-coil filament means a filament prepared by coiling a filament material into a helical structure (primary-coiled) with a small diameter and further coiling it into a helical structure (secondary-coiled) with a large diameter.
FIG. 4 is a schematic view that illustrates an example of the conventional electric lamp having a vertically positioned coiled-coil filament. FIG. 5 is an enlarged view of a part of the coiled-coil filament 102 shown in FIG. 4. As shown in FIG. 4, an electric lamp 101 in this example comprises a tube-like bulb 103 made of quartz glass or the like. The bottom of the bulb 103 is provided as a pinch-seal portion 104 and the top of the bulb 103 is provided as an exhaust seal portion 105. In the bulb 103, one end of a coiled-coil filament 102 made of, for example, tungsten is electrically connected to one end of an inner lead 106 and the other end of the filament 102 is electrically connected to a molybdenum film 108 being embedded in the pinch-seal portion 104. The filament 102 is arranged so as to extend substantially in parallel with an axis line of the bulb 103. In the bulb 103, the lead 106 extends substantially in parallel with the axis line of the bulb 103 and the other end of the lead 106 is electrically connected to the molybdenum film 107 being embedded in the pinch-seal portion 104. Furthermore, the pinch-seal portion 104 is planted with a pair of outer leads 109 and 110 and these leads are connected to the lead 106 and the coiled-coil filament 102 through the molybdenum films 107 and 108, respectively.
In the case of using an electric lamp having a coiled-coil filament as a backlight for a projector or the like, such electric lamp is co-operated with an optical system. Thus, it is preferable that the filament may be small as much as possible. In other words, it is preferable that the filament may be close to a point source of light as much as possible. In addition, if it is used as a heat source of RTP (rapid thermal processing) for a semiconductor device, there is a requirement for reducing the size of an electric lamp to reduce the size of the semiconductor device. For such a size reduction, for example, there is an idea of further lessening the space between the secondary-coiled coils of the coiled-coil filament without changing the surface area of the filament. However, if the space between the secondary-coiled coils is too narrowed, a short circuit may occur. Thus, there is a limit to lessen said space
Therefore, an object of the present invention is to provide an electric lamp having a coiled-coil filament with a further reduced size.
An electric lamp of the present invention for attaining the above object is one comprising a bulb and a coiled-coil filament accommodated in the bulb, characterized in that the coiled-coil filament consists of a core filament and an additional filament which is wound around the core filament and of which the diameter is smaller than the diameter of the core filament.
According to the present invention, a coiled-coil filament is formed as a double layer structure in which an additional filament with the diameter smaller than that of a core filament is wound around the core filament, so that the surface area of the coiled-coil filament per unit length can be increased, compared with the conventional filament having a diameter which is substantially equal to the sum of the diameter of the core filament and the diameter of the additional filament. Thus, the coiled-coil filament with a more reduced size can be obtained while the same initial characteristics as those of the conventional coiled-coil can be achieved. Consequently, the filament of the present invention can be closer to a point source of light, so that a higher efficient light emission can be achieved using the electric lamp of the present invention together with a reflecting mirror and an optical system, allowing not only the brighter electric lamp but also the size reduction of the electric lamp itself, compared with the conventional one. In addition, the electric lamp of the present invention improves the efficiency of light emission as mentioned above, so that electric power consumption can be reduced compared with the conventional one with respect to the same brightness, causing the economic effects thereof.
It is preferable that the core filament and the additional filament to be wound around the core filament may be made of the same material. Typically, tungsten is often used as a filament material. If tungsten is to be used as a material of the filament, both the core filament and the additional filament to be wound around the core filament may be preferably made of tungsten. According to the present invention, however, the filament material is not limited to tungsten and any material may be used.
The electric lamp of the present invention may be applied to a halogen lamp.
The coiled-coil filament in the electric lamp of the present invention may be arranged in the so-called vertical direction or arranged in the so-called horizontal direction.